It is hard to find a movement sequence in video footage that shows what I call the Ski Move from the optimal angle. In order to clearly see how a skier’s centre of mass rotates about the inside (uphill) edge of the inside ski and changes its position in relation to the inside ski when Shiffrin or Ligety start to step on it, the camera has to be looking at the racer head on. Since this sequence is almost impossible to find, I am going to try and create it in Poser.
The marked up sequence in the photo below shows how Shiffrin’s center of mass starts to rotate about the inside edge of her inside ski and into her new turn as she progressively steps on her new ski during the transition phase. As she does this, a point will be reached where her inside ski flattens on the snow. But it does not stop rotating at this point. Shiffrin’s momentum and the pressure she is applying to the ski cause it to change edges and begin to rotate into the new turn. As this is happening, Shiffrin is extending and moving forward in the hips. This drives the centre of pressure to the ball of her foot. The foot pronates and reinforces the rotation of the ski into the new turn. The circled images show where this happens. As Shiffrin’s foot pronates and the forces she is applying rotate her left ski into the new turn, she applies another layer of in-phase rotation with her hip rotators. These synchronized actions produce an over-centre mechanism that rotates her ski in multiple planes into the new turn.
There is a common perception that racers let their outside ski create all the turning effects. But the pivoting Shiffrin and Ligety apply at this key moment does much more than simply rotate the ski into the turn. It creates powerful forces that engage the external forces to drive the outside ski into the turn while creating a platform to balance on.